DESCRIPTION OF THE STATE OF THE ART
Much effort has been and is being focused on developing fuel conservation measures in general. One area in which particular effort has been directed to fuel conservation is greenhouse growing. Greenhouses customarily operate to accelerate and promote growth of plants by delivering large amounts of light, heat and moisture to plants.
Typically greenhouses are structures with light transparent roofs and in many cases, light transparent walls. Heat is provided for the greenhouses both by fuel consuming heaters and solar heat passing through the light transparent sections of the greenhouse.
One approach to fuel conservation in greenhouses has been directed to minimizing fuel consumption by the development of more efficient heat generation such as solar heat deflectors and heater systems capable of better heat distribution and temperature regulation.
Efforts have also been made to develop systems and apparatus for enhancing the insulation of greenhouses. The basic problem is that the sunlight desired and necessary for growing must not be markedly reduced by the insulation.
One attempt to insulate greenhouses is the inflated polyethylene double cover wherein two layers of very large sheets of polyethylene are draped over the outside of a greenhouse roof and provided with an internal air layer to form a heat insulation barrier. The apparatus is clumsy, laborious to assemble, exposed to the elements and reduces ventilation.
Interior insulation devices have also been developed. One device is a single fixed sheet, usually polyethylene, which has been arranged as a dropped roof at about eave height. A similar design of a movable sheet which can be rolled or drawn across the greenhouse at eave level as desired, has also been used. The former inimically obstructs light and reflects light outwardly and the latter collects the condensation and water leakage which is rained down on the plants when the sheet is drawn back for light exposure. Further, water on top of sheet makes movement of the sheet very difficult. The latter also has the disadvantage of harshly exposing the plants to the cold air blast from above the sheet since the sheet must be completely drawn to allow morning light passage before the air above the sheet can be warmed.
Another interior insulation system is the Clicon tube system designed for a controllable shading system wherein double inflatable tubes coated with aluminum are inflated and deflated to respectively block light and heat or to reflect light into the house.
Another effort using inflatable tubes has been tried with unsuccessful results. Inflatable uncoated polyethylene single tubes have been used with fiberglass roofs, and in a study conducted by R. L. Perry reported in Paper No. 75-4021 at the 1975 ASAE Annual Meeting was found to be too light obstructive for greenhouse application.